In case a workpiece is to be machined by a machine tool, for example, loads accompanying the machining in various directions are generally exerted between the machine tool and the workpiece, although depending upon the kinds of machining such as cutting or polishing, the material of the workpiece o the machining conditions. The loads act as reaction forces upon the machine tool and the workpiece. If the machine tool and the workpiece are completely fixed at the instant of machining, the machining can be ideally accomplished in a drastically improved precision.
In the case of machining of the workpiece using such machine tool, one of the machine tool or the workpiece is fixed whereas the other is moved by means of a mechanism such as a linear sliding bearing.
The linear sliding bearing to be used for this purpose is exemplified by one which comprises: a sliding bed having a section of generally inverted C-shape and including a horizontal portion and a pair of skirts depending downward from the two ends of the horizontal portion to form a recess at its lower side and formed in its inner sides with a pair of upper and lower load races extending longitudinally thereof and with relief ball tracks corresponding to the load races; a track base having its upper portion fitted in the recess of said sliding bed, while maintaining a predetermined spacing inbetween, and formed with rolling races corresponding to said load races; a pair of covers attached to the front and rear end faces of said sliding bed and formed in their inner sides with guide grooves for providing the communicating connections between the end portions of the load races and the relief ball tracks of said sliding bed to form endless ball tracks; a multiplicity of balls circulating in said endless ball tracks to bear the loads between the load races of said sliding bed and the rolling grooves of said track base; and gap adjusting means for adjusting the gap between said sliding bed and said track base to apply and adjust a pilot pressure (as disclosed in Japanese Patent Publications Nos. 61-34,934 and 61-48,009). Thus, the linear sliding bearing can bear the loads in the four directions, i.e., radial, inversely radial and rightward and leftward directions. In the linear sliding bearing of this kind, moreover, the rigidities in the four directions are enhanced by applying or adjusting the pilot pressure to the rollers to bear the four-directional loads to be generated between the machine tool and the workpiece during the machining, so that the accompanying chatter marks and vibrations may be suppressed as much as possible to improve the machining precision. In connection with the axial direction of the track base, on the other hand, what is principally aimed at is to lighten the loads upon the feeding drive system such as a feeder of screw and nut type or a linear motor mechanism. The rigidity necessary for the machining in the axial direction of the track base relies exclusively upon that of the feeding drive system.
Incidentally, the rigidity of the feeding drive system is determined, if the system is the feeder of screw and nut type, by the rigidity of the feed screw or nut itself, the rigidity of the support of the feed screw or nut, and the rigidity of the servo-motor for applying a rotating force to the feed screw. In order to increase the rigidity of the feeding drive system, it is necessary to enlarge the size of the feed screw or nut or to raise the driving force of the servo-motor. Thus, the increase in the rigidity of the feeding drive system is intrinsically limited by the problems which are caused by increasing the size of the apparatus or by raising the cost for the feeding drive system.
As various products are required to be the more precise accurate in the industry of recent years, a machine apparatus such as the machine tool for machining the products is required to have its machining precision improved the better. Thus, the linear sliding bearing taking a leading role for the machining precision of the various machine apparatus is requested to improve the machining precision.
It is, therefore, an object of the present invention to provide a linear sliding bearing which can have not only the rigidities of four directions, i.e., the radial, inversely radial, rightward and leftward directions but also a predetermined rigidity in the axial direction of the track base.
Another object of the present invention is to provide a linear sliding bearing which can apply the rigidity in the axial direction of the track base, if necessary, and adjust the level of the rigidity.
Still another object of the present invention is to provide a linear sliding bearing which is equipped with a lock mechanism capable of fixing the sliding bed in a target position when the sliding bed is moved along the track base to that position.
A further object of the present invention is to provide a linear sliding bearing which is enabled to accomplish the machining of high precision by adopting a machine apparatus such as a machine tool.